PTA is a common medical procedure used to widen a stenosis or constriction of the diameter of a bodily passage, such as an artery. When the procedure is applied to a coronary artery, it is referred to as percutaneous transluminal coronary angioplasty (PTCA); however, this procedure, as well as other similar medical procedures, may be applied to peripheral arteries, such as the carotid, or a wide variety of other vessels. It is common in such procedures to use a balloon delivery catheter in conjunction with an intravascular prosthesis or stent. One or more dilation balloons may be used to widen the artery at the point of occlusion, and a subsequent balloon is used to position the stent at the proper location. The balloon is inflated to expand the stent to its working diameter, and is sized (often by another balloon) to implant the stent into the vascular wall. Plastic deformation of the stent prevents it from collapsing once the balloon has been deflated and removed from the patient. The stent is typically metallic and may comprise stainless steel or tantalum, for example. Thus, restenosis is resisted by the stent.
In order to adequately attach the unexpanded stent onto the balloon catheter for delivery into the patient, without having the stent come off the balloon prematurely, the stent is "crimped" or otherwise radially collapsed sufficiently to attach it to the balloon. It is typical in some countries for this crimping to be performed manually by the physician in the catheter laboratory. However, there is the risk that too much or too little pressure may be applied and the balloon and/or stent may be damaged, lost, or may not otherwise perform as desired during the procedure. On the other hand, there is the opposite risk that the physician will not apply enough crimping pressure to the stent to load it onto the balloon, thus allowing it to slip or rotate on the catheter during deployment, or to come off entirely, leading to a possibly catastrophic result. Accordingly, in other countries, stents are required by regulation to be crimped onto their associated delivery balloon at the time of production by the manufacturer; such "preattached" stents enjoying the benefits of production quality control procedures.
This problem is addressed by U.S. Pat. No. 5,437,043 to Williams et al., which discloses a production stent-loading mechanism designed to automatically load a stent onto the distal end of a catheter assembly with a minimum of human handling, with the goal of more securely attaching the stent onto the catheter. In one embodiment of this mechanism, a tubular member with an inner inflatable bladder receives a balloon catheter having a stent positioned over the uninflated balloon. Inflation of the bladder causes an annular portion of the bladder surrounding the stent to crimp the stent onto the balloon. Assuming accurate calibration of the pressurization device, a uniform crimping pressure will be applied to the stent to secure it to the uninflated balloon. In other embodiments, plates moving relative to one another exert a similar uniform crimping pressure to the cylindrical exterior surface of the stent. Thus, in this device, if the maximum and minimum crimping pressures are not carefully regulated, the stent could either fall off or become damaged, respectively. Such precise pressure regulation undoubtedly adds greatly to the cost of stent/catheter production, not to mention the complexity of the mechanism itself. In addition, however, with such preattached stents, the physician's option to use alternate delivery balloons is severely restricted, as it is left completely to the discretion of the stent manufacturer.
Thus, in the absence of more secure manual loading mechanisms and methods, only preattached stents and balloon catheters are available for a physician's use in some countries. Although this may obviate the need for manual attachment by the physician, thus achieving a higher degree of safety, the physician no longer has the option to choose the most suitable balloon catheter and preferred stent for a particular patient's needs.
Therefore, there is a need for nonproduction stent loading devices and techniques which allow greater freedom and flexibility in stent and balloon catheter combinations, as well as for production devices which will more securely load a stent onto the catheter without requiring precise pressure regulation.